The present invention relates generally to rail vehicle air brakes and more specifically, to a fluid operated parking brake therefore.
The brakes for railroad vehicles are pneumatic operated brakes, or air brakes which include a brake cylinder to operate the brake shoes to engage the wheel and brake the car. The brake cylinder receives a pneumatic signal to apply the brakes and generally has a spring return. Other brake cylinders may be spring applied and air released. Most railroad cars also include a parking or hand brake, which is a manually operated device which applies the brake manually. For truck mounted brake riggings, the hand brake is generally applied to the output of the brake cylinder and more specifically to the levers which connect the brake cylinder to the brake beams. A typical example is shown in U.S. Pat. No. 5,069,312. Chains are generally connected to the levers and to a convenient place on the car to allow the manual application of the parking brake. Another example of a truck mounted brake includes brake cables which are actuated manually and remotely and are connected to the piston of the brake cylinder to manually operate the brake cylinder. A typical example is shown in U.S. Pat. No. 4,653,812 and similarly illustrated in FIGS. 1 and 2 to be assessed below. Another mechanical system for a hand brake at the output of the brake cylinder is illustrated in U.S. Pat. No. 4,019,426.
The integration of the air brake control of the brake cylinder and a manual, pneumatic and/or electropneumatic controlled parking brake is illustrated in U.S. Pat. No. 5,738,416. In one embodiment illustrated in FIGS. 7 and 8, the piston rod of the modified brake cylinder to include recess to receive a latching detent controlled by a piston rod of a latching cylinder. This mechanism latches the brake in the applied position and requires a release signal to remove the detent. Thus, in even normal braking conditions, the detent is actuated.
Manual pumps to actuate separate hydraulic parking brakes on railroad vehicles are illustrated in U.S. Pat. No. 5,701,975. The parking brakes are connected to the brake beams and are independent of the normal brake cylinder.
The present invention is a fluid parking brake for a rail vehicle having a brake cylinder with a first piston responsive to fluid signals to apply and release the brakes on the vehicle. The parking brake includes a housing having a second piston in the housing and which is coupled to the first piston. An apply port in the housing receives a pressure signal to move the second piston to an apply position. A detent is provided for holding the second piston in the applied position.
The detent may be responsive to removal of pressure at the applied port to hold the second piston in the applied position. Release of the detent allows the second piston to move to the release position. A release port may be provided in the housing for receiving a pressure signal to release the detent and allow the second piston to move to the release position. The detent may also be released by manual force on the detent. A lost motion device may be provided connecting the second piston to the first piston. This allows the first piston to move in an applied direction without moving the second piston in its applied direction.
The detent may include at least one recess on the second piston and a dog to be received in the recess to hold the second piston in the applied position. A lock on the detent is responsive to the removal of pressure at the applied port to lock the dog in the recess. The lock includes a third piston having a cam recess and the dog rides in the cam recess. The third piston is responsible to the removal of pressure at the applied port to lock the dog in the recess and is responsive to pressure at the release port to unlock the dog and allow the second piston to move to the release position.
The housing of the parking brake may be cylindrical and mounted to the brake cylinder. A pair of parking brakes may be provided with their second pistons connected to the first piston symmetrical with respect to the axis of travel of the first piston. The brake cylinder may include an integral slack adjuster. A manually operated pump is connected fluidically to the applied port and may be a hydraulic pump with automatic depressurization.
The brake cylinder and the first piston have openings for receiving cables of a hand brake. The second piston is connected to the first piston via these openings. Thus, a method for retrofitting a cable operated parking brake for a rail brake cylinder using a fluidly operated parking brake would include connecting the second piston of the parking brake via the openings in the first housing and the first piston which receive the parking brake cable. Preferably, this includes connecting the second piston to the first piston by a lost motion device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.